1. Field of the Invention
This invention relates to an apparatus and a process for assisting the mounting of a tire-wheel assembly onto an. More particularly it relates to an apparatus and a process for assisting the mounting of a tire-wheel assembly onto an axle which can easily conduct the mounting of the tire-wheel assembly onto the axle of a vehicle in a short time while precisely arranging a center of a rotating axis in the tire-wheel assembly with a center of the axle in the vehicle in a straight line and can largely contribute to improve vibration properties in the running of the vehicle and resistance to uneven wear of the tire and is particularly possible to hold adequately corrected static and dynamic unbalancing quantities in the tire-wheel assembly even after the assembly is mounted onto the vehicle.
2. Description of the Related Art
An outline of mounting the tire-wheel assembly onto the axle of the vehicle will be described below with reference to FIG. 7 illustrating a partial sectional view of a main mounting portion.
As shown in FIG. 7, a slight clearance is formed in a hub hole (center hole) in a wheel disc portion 3d of the tire-wheel assembly (not shown) with respect to a cylindrical protrusion 5a in a hub 5 of the axle side, so that the tire-wheel assembly is applied onto the hub 5 by passing plural hub bolts 6 (4-6 bolts in case of a passenger car) equally disposed on the hub 5 at a given pitch circle diameter (PCD) through respective bolt holes 9 formed in the disc portion 3d at the same PCD.
Then, a fastening nut 7 is screwed around each of the hub bolts 6 and is sufficiently clamped to fully contact the disc portion 3d to a contacting surface 5b of the hub 5 or fully contact a projecting portion formed around the bolt hole 9 to the contacting surface 5b in the illustrated embodiment. Thus the mounting of the tire-wheel assembly onto the axle is completed.
As shown in FIG. 7, a tip portion of the fastening nut 7 mainly used in light vehicle, passenger car and small size truck has a taper seat 8, while the bolt hole 9 of the disc portion 3d has a taper seat having a shape corresponding to the shape of the taper seat 8. When clamping the nut 7, therefore, the taper seat of the tip portion of the nut 7 and the taper seat of the bolt hole 9 themselves act to exhibit a centering behavior with each other. Consequently, the tire-wheel assembly can adequately be mounted onto the axel of the vehicle without eccentricity from a center Cx of the axel.
Instead of the centering through the taper seat, a spherical seat (not shown) is formed in the tip portion of the nut 7 and also a seat having the same spherical shape as in the tip portion is formed in the bolt hole, whereby the adequate mounting of tire-wheel assembly onto the axel is practiced. Further, the mounting of the tire-wheel assembly through a so-called wheel bolt instead of the fastening nut 7 is widely carried out, in which a taper seat having the same shape as in the taper seat 8 of the nut 7 is formed on the head portion of the bolt for conducting the centering.
There are well-known the following three methods of clamping the fastening nut 7 or the wheel bolt in the mounting of the tire-wheel assembly onto the axel.
Firstly, there is a general method wherein the fastening nut 7 or the wheel bolt is usually screwed to a certain extent every one through a wrench and then clamped under a given uniform torque through a torque wrench.
Secondly, there is a method of simultaneously clamping plural fastening nuts 7 or the wheel bolts through a specific torque wrench, which is a special method adopted by automobile manufacturers aiming at the reduction of time required for the mounting of the tire-wheel assembly.
Thirdly, there is a method suitable for skilled workers wherein the fastening nut 7 or the wheel bolt is gradually clamped at positions corresponding to a diagonal line or opposite positions near thereto until the loosening of the nut 7 or the wheel bolt is removed while striking a tire of the tire-wheel assembly by hand or rotating the assembly and then the nuts 7 or the wheel bolts located at opposite positions are completely clamped through the torque wrench.
The tire-wheel assembly has a fairly heavy weight. For example, when the tire is a radial tire for passenger car having a tire size of 205/65R15 and the wheel is an aluminum wheel having a rim contour of 51/2J, the tire-wheel assembly has a weight of about 15 kg. Since a braking device for the vehicle should be arranged inside the tire-wheel assembly, the disc portion 3d of the wheel contacting with the hub 5 is offset toward the outside of the vehicle irrespectively of passenger car and truck and bus. As a result, it is obliged that the center of gravity in the tire-wheel assembly as a whole shifts at a position outward from an equatorial plane of the tire dividing the tire into two parts in the widthwise direction thereof.
Since the total weight of the tire-wheel assembly is heavy and the center of gravity of the assembly is offset outward from the mounting position, moment of shifting the center of gravity downward from the center of rotating axis in the axle of the vehicle always acts to the tire-wheel assembly at a state of contacting with the hub 5. When the fastening nut 7 or the wheel bolt is more clamped at such a state, the above moment overcomes the guiding action of the taper seat or spherical seat and hence both the centers of the rotating axis of the vehicle axle and the tire-wheel assembly become eccentric with each other without being arranged in the same straight line. That is, the tire-wheel assembly is mounted onto the vehicle axle at an eccentric state of the center of gravity of the assembly from the center of the rotating axis of the vehicle axel.
When the vehicle is run at such an eccentric state, exciting force is applied to the vehicle from unspringing position to create vibrations on the vehicle and also exciting force is applied to the tread rubber of the tire to create uneven wear. As a result, the effect of correcting static and dynamic unbalance quantities of the tire-wheel assembly to zero or near to zero before the mounting onto the vehicle for the control of vibrations during the running of the vehicle and the prevention of uneven wear of the tread rubber is largely damaged and also the vibration properties and the resistance to uneven wear in the vehicle provided with the tire-wheel assembly having insufficient corrected unbalance quantities are considerably degraded.
If the eccentric quantity is large, the exciting force creates a considerably large stress in the hub bolt 6 in addition to the simple degradation of the vibration properties in the high-speed running. In this case, the bolt 6 or the nut 7 is galled or occasionally creates fatigue breakage under the action of large repetitive stress and hence there is caused a fear of falling off the tire from the vehicle during the running. This tendency becomes remarkable when the weight of the tire-wheel assembly is heavy.
The relationship among the vibration of the vehicle, uneven wear of the tread rubber and the aforementioned mounting methods of the tire-wheel assembly onto the axle is investigated by comparison among the first to third methods, from which it is confirmed that the third method is superior to the first and second methods in accordance with the worker. However, the mounting work by the third method takes a long time and requires intuition based on the skilled worker's experience and also the scattering between the workers is large, so that it can not be said that the third method is general.